Experiences with the use of stabilisation geogrids in demonstrating an improvement in bearing capacity of recycled materials

Abstract

The use of recycled granular materials for road construction should be a necessity in current times; both for economic and environmental reasons. By the use of such materials, the road construction industry helps to protect natural resources and reduce its carbon footprint, while lowering the cost of pavement construction. However, the use of recycled materials can often raise concerns, viz. design compliance, low homogeneity, perceived lower quality and an onerous production process when compared to the use of virgin materials. It may be common practice for the variability in the engineering parameters of these materials to influence designers to specify thicker pavement layers in order to ensure that the required bearing capacity and/or design life of the road is achieved. The use of hexagonal stabilisation geogrids may provide a method of mitigating against the loss of homogeneity and improve the engineering parameters of recycled granular materials. The case-studies presented herein demonstrate that the mechanical stabilisation of recycled granular materials with a hexagonal geogrid, results in an increased stiffness of the layer and significantly aids compaction. When aggregate is placed and compacted on a stiff hexagonal geogrid, aggregate particles interlock within the geogrid apertures and are confined by its stiff ribs. A composite mechanically stabilised layer (MSL) is created, in which the geogrid and aggregate act in unison. Lateral restraint, provided by the geogrid, reduces strain within the aggregate skeleton and thereby increases the stiffness of the layer. The result is that the required performance parameters, be it a bearing capacity of a layer and/or life of the pavement, can be successfully achieved with the use of, and possible reduction in the required layer thickness of, recycled granular materials. The concept of mechanical stabilisation of aggregate layers by the use of geogrids is detailed in this paper. Furthermore, several case studies are presented which demonstrate the use of hexagonal stabilisation geogrids to improve the bearing capacity of various recycled materials such as recycled asphalt, recycled concrete, and coal mine shales.